Various techniques have been utilized to separate suspended particles from liquids including coagulation, flocculation, sedimentation, filtration and cyclonic separation. For example, in a typical hydroclone embodiment, pressurized feed liquid is introduced into a conically shaped chamber under conditions that create a vortex within the chamber. Feed liquid is introduced near the top of a conical chamber and an effluent stream is discharged near the bottom. Centrifugal forces associated with the vortex urge denser particles towards the periphery of the chamber. As a result, liquid located near the center of the vortex has a lower concentration of particles than that at the periphery. This “cleaner” liquid can then be withdrawn from a central region of the hydroclone. Examples of hydroclones are described in: U.S. Pat. No. 3,061,098, U.S. Pat. No. 3,529,544, U.S. Pat. No. 4,414,112, U.S. Pat. No. 5,104,520, U.S. Pat. No. 5,407,584 and U.S. Pat. No. 5,478,484. Separation efficiency can be improved by including a filter within the chamber such that a portion of the liquid moving to the center of the chamber passes through the filter. In such embodiments, cyclonic separation is combined with cross-flow filtration. Examples of such embodiments are described in: U.S. Pat. No. 7,632,416, U.S. Pat. No. 7,896,169, U.S. Pat. No. 8,201,697 and US2012/0010063.
Size and separation efficiency are limiting factors for any given separation system. For example, while flocculation and sedimentation techniques are relatively energy efficient, they typically require settling ponds and long separation times. Hydroclones offer a smaller footprint, but have higher energy demand and are less effective at removing small particulate matter. Cross-flow filtration systems are small and produce high quality separations but are prone to fouling and are energy intensive. New systems are sought which offer an improved balance of attributes including overall size, separation efficiency and energy efficiency.